1. Field of the Invention
This invention relates to disk drive components, and more particularly, to actuators of a new design for combination into head stack assemblies of multiple head gimbal assemblies. Specifically, the invention relates to improvements in the configuration of actuator arms to minimize the net variation in gram load resulting from staking operations during assembly of the head stack.
2. Related Art
An actuator is a mechanism for moving disk drive suspensions arcuately or linearly into position at a disk surface. See FIG. 3 PRIOR ART. The actuator E-block 4 has one or more arms 5 to which the head gimbal assembly load beams 6 are attached, usually two load beams per arm, one above, the upper load beam, and one below, the lower load beam. The load beams are fixed by welding to the planar base 7 of a mounting plate 8 that has an annular boss 9 rising from the base. The lower load beam is attached to a lower mounting plate base and the lower mounting plate boss is inserted into the lower opening of a bore that extends through the arm from its lower face to its upper face. An upper mounting plate boss is similarly inserted into the arm bore upper opening with a load beam attached. The upper and lower mounting plates thus are reversed in orientation and have their respective bosses opposed and differently affected by staking operations. The terms upper and lower herein as applied to mounting plates have reference to the direction of staking. Thus the mounting plate that is closer to the origin of the staking movement is the upper mounting plate and the mounting plate that is closer to the destination of the staking movement is the lower mounting plate.
To secure the oppositely directed mounting plates to the actuator arm, the mounting plate bosses are radially expanded to engage the bore interior wall. A slightly oversize staking tool, such as staking ball 10, is passed through the central opening of the annular bosses 9 to force the boss outward and into bore interior wall engagement.
There is in addition to the radial force being exerted a downward axial force associated with the movement of the staking tool, and this force has a different effect on the upward facing (lower) mounting plate (tends to go convex toward the bore) from its effect on the downward facing (upper) mounting plate (tends to go concave toward the bore). These different effects cause different and difficult to control changes in the shape of the mounting plates and their intended suspension gram preloads.